This invention relates generally to melt distribution arrangements for injection moulding apparatus. More particularly, this invention relates to cross over nozzle arrangements for multi-level stack moulds.
In injection moulding apparatus utilizing a stack mould design, a melt transfer system is required which transfers melt across mould levels yet which is separable to enable mould separation. The separable component of the melt transfer system is referred to as a xe2x80x9ccross over nozzlexe2x80x9d.
In order to be effective, a cross over nozzle is provided with some means for blocking melt flow upon separation. Prior art systems include a valve gate design such as described in U.S. Pat. No. 4,212,626, a hot probe design such as described in U.S. Pat. No. 4,891,001 and a valveless melt transfer system such as described in U.S. Pat. No. 5,458,843. Each such system has particular benefits for certain types of application. Each however typically drools or leaks in one way or another.
The valve gate design utilizes a pair of nozzles which are pressed up one against the other when the mould is closed with respective nozzle orifices in registry. Each nozzle orifice has a pin which can be advanced to block its respective orifice or retracted to unblock the orifice and permit melt flow. A disadvantage with this arrangement is that a positive driving force is required for the pin, which can be mechanical, pneumatic or hydraulic. The driving mechanisms typically require a considerable amount of space and accordingly such an arrangement may not be useable in some applications due to space constraints. There is also typically some stringing at the gate with such an arrangement. As the two pins open and close in a hot resin environment, hot resin may be trapped between the two pins causing a string to form when the mould is opened.
The hot probe design basically utilizes a heated nozzle tip to selectively allow the resin to solidify and block the nozzle or melt to free the nozzle. As it lacks a valve pin it has a tendency to drool heavily yet has the advantage of being compact and accordingly suited to an arrangement where space is limited.
The valveless melt transfer design includes an expansive chamber which captures melt during mould opening. This is an effective system which requires minimal shut height yet still causes some angel hair stringing.
It is an object of the present invention to provide a cross over nozzle arrangement with virtually no drool which can operate in a small volume similar to that of a valveless melt transfer system to enable its use on three and four-level stack mould systems.
According to the present invention, a cross over nozzle is provided of two parts which, when joined, define a housing having a passage extending therethrough, a tapered valve seat extending about the passage and a valve member having a tapered valve head disposed in the passage for engaging the valve seat. The two parts are axially separable at an interface extending through the valve seat/valve head. In order to open the valve, both valve parts are first joined and then moved together as one member in the same direction relative to the housing axially away from the valve seat. Similarly, the valve members are jointly moved into engagement with the valve seat before the cross over nozzle is separated. Accordingly, unlike the valve gate design, the valve interface between the two parts of the valve head isn""t exposed to molten resin and therefore molten resin isn""t trapped therebetween to cause a string upon opening.
More particularly, a cross over nozzle is provided which has a nozzle housing with the melt passage extending therethrough, a valve axis extending along the passage and a tapered valve seat in the passage extending about the valve axis. The nozzle housing has a first housing part and a second housing part separable along the valve axis through the valve seat at a housing interface. A first valve seat part is carried by the first housing part and a second valve seat part is carried by the second housing part. A valve member having a tapered valve head is disposed in the passage and axially movable relative to the nozzle housing between a closed configuration wherein the valve head engages the valve seat to block melt flow along the passage and an open configuration wherein the valve head is displaced from the valve seat to allow melt flow along the passage about the valve head. The valve head has a first valve head part and a second valve head part which meet at a valve interface corresponding to the nozzle interface and at which the valve member is separable along the axis into first and second valve parts for respectively sealing the first and second nozzle parts in the closed configuration. A valve opening actuator acting between the valve member and the nozzle housing is provided for causing simultaneous movement of the first and second valve parts relative to the nozzle housing toward the open configuration when said first and second nozzle housing parts and first and second valve parts are joined. A first valve closing actuator is provided which acts between the first valve part and the first housing part to bias the first valve part toward its closed configuration. A second valve closing actuator is provided which acts between the second valve part and the second housing part to bias the second valve part towards its closed configuration.
According to one embodiment, the valve opening actuator may be a fluid pressure responsive first piston in a bore associated with a first housing part. A first valve stem may extend between and operably connect the first piston and the first valve head part. The first piston may also act as the first valve closing actuator. A fluid pressure responsive second piston and a second bore associated with a second housing part may act as the second valve closing actuator. A second valve stem may extend between and operably connect the second piston and the second valve head part.
According to an alternate embodiment, the first housing part may have a base part and an outer part which are telescopically connected for relative axial movement along the nozzle axis. A biasing means may act between the base part and the outer part to urge the outer part away from the base part. The first valve seat part may be carried by the outer part. A first valve stem may extend between and rigidly secure the first valve head part and the base part. The first valve head part may engage the seat to limit movement of the outer part away from the inner part. The valve opening actuator may cause movement of the second housing part toward the first housing part and act against the biasing means to urge the outer part of the first housing part toward the base part in turn causing relative movement of the valve head and valve seat to move the valve member into the open configuration. The biasing means between the base part and the outer part of the first housing part may also act as the first valve closing actuator. A second valve stem may extend between and operably connect the second valve head part with the second closing actuator.
The biasing means in the alternate embodiment described in the preceding paragraph may be at least one of a resilient biasing means and fluid pressure. The second valve closing actuator may be at least one of a resilient biasing means and a fluid pressure responsive piston in a bore associated with the second housing part.